Storage facilities for digital information are a critical resource. The demand for storage space for both conventional data, such as text documents and other human readable files, and multimedia streams, such as audio and/or video data, has increased significantly. Such an increase results from a number of different factors, such as legal requirements to store and maintain certain types of information; an increase in the different types of data which are being stored; and even an increase in the size of individual units of data, such as word processing document files, video data files and so forth. This increased demand has in turn resulted in a higher demand for storage space, and in particular for storage space which is accessible “on-line”.
As the demand for on-line storage space increases, a number of options are possible to fulfill that demand. For example, additional hardware, such as magnetic media devices (“hard disk drives”), may be purchased to increase the available amount of electronically accessible storage space. However, as the quantity of such hardware devices increases, the management problem for electronic management of these devices also increases. Furthermore, merely increasing the storage space may be both wasteful and unnecessary, since not all of the data may be required, or at least not required for immediate access.
The problem may be partially alleviated through the use of a mixture of different types of storage facilities. For example, on-line storage refers to direct-access, permanently mounted storage areas, such as magnetic (or other types of media) disk drives and disk arrays. The time required for access to such storage areas to be made is typically measured in fractions of a second. On line storage is fast, but is also expensive, and therefore may not be available for the entire amount of storage needed by an organization. Since not all data may need to be stored in on-line storage, near-line storage is available however for customer use. Near-line storage is based upon an automatically (machine) operated storage area, such as optical disks residing on a disk “jukebox” or tapes in an automatic tape library. Such automatically operated storage devices are able to store and automatically access a relatively large amount of data with fewer physical reading devices, or drives, for reading the data. This type of storage is less expensive, but also somewhat slower for accessing the data, such that access times are measured in seconds to minutes, or even longer, depending upon the availability of physical drives for reading the storage media. On-line or near-line storage may also feature a system with a plurality of physical drives, connected together, for example in a LAN (local area network) or WAN (wide area network).
Off-line storage is the least expensive type of storage, but is also the slowest for access, as it does not permit automatic electronic access. Instead, manual operation of the storage devices and physical drives is required by a human operator. The number of physical drives is greatly reduced compared to the number of storage devices (or at least the amount of available storage space). However, the access time for data from such devices is measured from minutes to hours, depending upon the availability of the human operator and the location of the storage devices, as well as the availability of the physical drives.
Other types of storage devices and functions may also be used, in addition to, or in replacement for, the above-described devices and functions. In any case, the difficulty with a mixed system, or a system in which different types of storage areas (topology) are used, with different types of storage devices and different accessibility (particularly with regard to access time) and/or capacity, is the management of the data. Certain types of data may be more important, or at least more time-critical for access, such that the access time may be very important for some types of data, and much less important for other types of data. In addition, the importance of data, and therefore the retention policy regarding this data may change over time, and have to be appropriately handled in the system. Cost is also an important factor. Also, decisions must be made concerning the number and type of storage devices to be purchased, along with any required supporting devices and/or system support, such as human operators for example. Currently, these systems are designed and constructed manually, and decisions are made on the basis of some type of policy. However, the operation of the actual system and even the design itself may not be optimal for a particular organization.